2.6 Modularity assessment methods
In the evaluation of modularity of contiguous skull landmarks based on the hypothesis that covariance between true modules (embryologic relations) should be lower than for other developmentally unrelated parts, the extent of such covariation is expressed in terms of the RV coefficients; RV coefficient (Relative variance); as explained by Escoufier (1973); is a similarity coefficient between positive semi-definite matrices or simply a multivariate generalization of the squared Pearson correlation coefficient (values between 0 and 1), it measures two sets of points that may be represented in a matrix; the closer to 1 the RV becomes, the more similar the two matrices. The eleven dorsal view landmarks were divided into two subsets of equal number of landmarks; only landmarks forming contiguous configurations were allowed to run with full enumerations of partitions using MorphoJ software vers. 2.0 (Rholf, 2015) (MorphoJ is available freely under the Apache Licence, Version 2.0, from the web site http://www.flywings.org.uk/MorphoJ_page.htm)